Add support for enabling/disabling touch events:

- switch between gestures and touch events
 - improved performance as we don't need to listen always

source/SkiaSharp.Views.Forms/SkiaSharp.Views.Forms.Android/SKTouchHandler.cs

@@ -14,18 +14,22 @@ namespace SkiaSharp.Views.Forms
 			this.scalePixels = scalePixels;
 		}
 
-		public void Attach(View view)
+		public void SetEnabled(View view, bool enableTouchEvents)
 		{
-			view.Touch += OnTouch;
+			if (view != null)
+			{
+				view.Touch -= OnTouch;
+				if (enableTouchEvents)
+				{
+					view.Touch += OnTouch;
+				}
+			}
 		}
 
 		public void Detach(View view)
 		{
 			// clean the view
-			if (view != null)
-			{
-				view.Touch -= OnTouch;
-			}
+			SetEnabled(view, false);
 
 			// remove references
 			onTouchAction = null;

source/SkiaSharp.Views.Forms/SkiaSharp.Views.Forms.Mac/SKTouchHandler.cs

@@ -16,18 +16,25 @@ namespace SkiaSharp.Views.Forms
 			this.scalePixels = scalePixels;
 		}
 
-		public void Attach(NSView view)
+		public void SetEnabled(NSView view, bool enableTouchEvents)
 		{
-			view.AddGestureRecognizer(this);
+			if (view != null)
+			{
+				if (enableTouchEvents && !view.GestureRecognizers.Contains(this))
+				{
+					view.AddGestureRecognizer(this);
+				}
+				else if (!enableTouchEvents && view.GestureRecognizers.Contains(this))
+				{
+					view.RemoveGestureRecognizer(this);
+				}
+			}
 		}
 
 		public void Detach(NSView view)
 		{
 			// clean the view
-			if (view != null)
-			{
-				view.RemoveGestureRecognizer(this);
-			}
+			SetEnabled(view, false);
 
 			// remove references
 			onTouchAction = null;

source/SkiaSharp.Views.Forms/SkiaSharp.Views.Forms.Native.Shared/SKCanvasViewRendererBase.cs

@@ -51,6 +51,13 @@ namespace SkiaSharp.Views.Forms
 #endif
 		}
 
+#if __IOS__
+		protected void SetDisablesUserInteraction(bool disablesUserInteraction)
+		{
+			touchHandler.DisablesUserInteraction = disablesUserInteraction;
+		}
+#endif
+
 		protected override void OnElementChanged(ElementChangedEventArgs<TFormsView> e)
 		{
 			if (e.OldElement != null)
@@ -71,11 +78,11 @@ namespace SkiaSharp.Views.Forms
 				{
 					var view = CreateNativeControl();
 					view.PaintSurface += OnPaintSurface;
-					touchHandler.Attach(view);
 					SetNativeControl(view);
 				}
 
 				// set the initial values
+				touchHandler.SetEnabled(Control, e.NewElement.EnableTouchEvents);
 				Control.IgnorePixelScaling = e.NewElement.IgnorePixelScaling;
 
 				// subscribe to events from the user
@@ -88,7 +95,7 @@ namespace SkiaSharp.Views.Forms
 
 			base.OnElementChanged(e);
 		}
-		
+
 #if __ANDROID__
 		protected override TNativeView CreateNativeControl()
 		{
@@ -105,10 +112,14 @@ namespace SkiaSharp.Views.Forms
 		{
 			base.OnElementPropertyChanged(sender, e);
 
-			if (e.PropertyName == nameof(SKFormsView.IgnorePixelScaling))
+			if (e.PropertyName == SKFormsView.IgnorePixelScalingProperty.PropertyName)
 			{
 				Control.IgnorePixelScaling = Element.IgnorePixelScaling;
 			}
+			else if (e.PropertyName == SKFormsView.EnableTouchEventsProperty.PropertyName)
+			{
+				touchHandler.SetEnabled(Control, Element.EnableTouchEvents);
+			}
 		}
 
 		protected override void Dispose(bool disposing)

source/SkiaSharp.Views.Forms/SkiaSharp.Views.Forms.Native.Shared/SKGLViewRendererBase.cs

@@ -51,6 +51,13 @@ namespace SkiaSharp.Views.Forms
 #endif
 		}
 
+#if __IOS__
+		protected void SetDisablesUserInteraction(bool disablesUserInteraction)
+		{
+			touchHandler.DisablesUserInteraction = disablesUserInteraction;
+		}
+#endif
+
 		protected override void OnElementChanged(ElementChangedEventArgs<TFormsView> e)
 		{
 			if (e.OldElement != null)
@@ -75,10 +82,11 @@ namespace SkiaSharp.Views.Forms
 #else
 					view.PaintSurface += OnPaintSurface;
 #endif
-					touchHandler.Attach(view);
 					SetNativeControl(view);
 				}
 
+				touchHandler.SetEnabled(Control, e.NewElement.EnableTouchEvents);
+
 				// subscribe to events from the user
 				newController.SurfaceInvalidated += OnSurfaceInvalidated;
 				newController.GetCanvasSize += OnGetCanvasSize;
@@ -111,6 +119,10 @@ namespace SkiaSharp.Views.Forms
 			{
 				SetupRenderLoop(false);
 			}
+			else if (e.PropertyName == SKFormsView.EnableTouchEventsProperty.PropertyName)
+			{
+				touchHandler.SetEnabled(Control, Element.EnableTouchEvents);
+			}
 		}
 
 		protected override void Dispose(bool disposing)
@@ -159,7 +171,7 @@ namespace SkiaSharp.Views.Forms
 		private void OnPaintSurface(object sender, SKNativePaintGLSurfaceEventArgs e)
 		{
 			var controller = Element as ISKGLViewController;
-			
+
 			// the control is being repainted, let the user know
 			controller?.OnPaintSurface(new SKPaintGLSurfaceEventArgs(e.Surface, e.RenderTarget));
 		}

source/SkiaSharp.Views.Forms/SkiaSharp.Views.Forms.Shared/SKCanvasView.cs

@@ -7,7 +7,10 @@ namespace SkiaSharp.Views.Forms
 	public class SKCanvasView : View, ISKCanvasViewController
 	{
 		public static readonly BindableProperty IgnorePixelScalingProperty =
-			BindableProperty.Create(nameof(IgnorePixelScaling), typeof(bool), typeof(SKCanvasView), default(bool));
+			BindableProperty.Create(nameof(IgnorePixelScaling), typeof(bool), typeof(SKCanvasView), false);
+
+		public static readonly BindableProperty EnableTouchEventsProperty =
+			BindableProperty.Create(nameof(EnableTouchEvents), typeof(bool), typeof(SKCanvasView), false);
 
 		// the user can subscribe to repaint
 		public event EventHandler<SKPaintSurfaceEventArgs> PaintSurface;
@@ -37,6 +40,12 @@ namespace SkiaSharp.Views.Forms
 			set { SetValue(IgnorePixelScalingProperty, value); }
 		}
 
+		public bool EnableTouchEvents
+		{
+			get { return (bool)GetValue(EnableTouchEventsProperty); }
+			set { SetValue(EnableTouchEventsProperty, value); }
+		}
+
 		// the user asks to repaint
 		public void InvalidateSurface()
 		{

source/SkiaSharp.Views.Forms/SkiaSharp.Views.Forms.Shared/SKGLView.cs

@@ -7,7 +7,10 @@ namespace SkiaSharp.Views.Forms
 	public class SKGLView : View, ISKGLViewController
 	{
 		public static readonly BindableProperty HasRenderLoopProperty =
-			BindableProperty.Create("HasRenderLoop", typeof(bool), typeof(SKGLView), default(bool));
+			BindableProperty.Create("HasRenderLoop", typeof(bool), typeof(SKGLView), false);
+
+		public static readonly BindableProperty EnableTouchEventsProperty =
+			BindableProperty.Create(nameof(EnableTouchEvents), typeof(bool), typeof(SKCanvasView), false);
 
 		public bool HasRenderLoop
 		{
@@ -15,9 +18,15 @@ namespace SkiaSharp.Views.Forms
 			set { SetValue(HasRenderLoopProperty, value); }
 		}
 
+		public bool EnableTouchEvents
+		{
+			get { return (bool)GetValue(EnableTouchEventsProperty); }
+			set { SetValue(EnableTouchEventsProperty, value); }
+		}
+
 		// the user can subscribe to repaint
 		public event EventHandler<SKPaintGLSurfaceEventArgs> PaintSurface;
-	
+
 		// the user can subscribe to touch events
 		public event EventHandler<SKTouchEventArgs> Touch;
 
@@ -49,7 +58,7 @@ namespace SkiaSharp.Views.Forms
 		{
 			PaintSurface?.Invoke(this, e);
 		}
-	
+
 		// the native view responds to a touch
 		protected virtual void OnTouch(SKTouchEventArgs e)
 		{

source/SkiaSharp.Views.Forms/SkiaSharp.Views.Forms.UWP/SKTouchHandler.cs

@@ -17,19 +17,8 @@ namespace SkiaSharp.Views.Forms
 			this.scalePixels = scalePixels;
 		}
 
-		public void Attach(FrameworkElement view)
+		public void SetEnabled(View view, bool enableTouchEvents)
 		{
-			view.PointerEntered += OnPointerEntered;
-			view.PointerExited += OnPointerExited;
-			view.PointerPressed += OnPointerPressed;
-			view.PointerMoved += OnPointerMoved;
-			view.PointerReleased += OnPointerReleased;
-			view.PointerCanceled += OnPointerCancelled;
-		}
-
-		public void Detach(FrameworkElement view)
-		{
-			// clean the view
 			if (view != null)
 			{
 				view.PointerEntered -= OnPointerEntered;
@@ -38,7 +27,22 @@ namespace SkiaSharp.Views.Forms
 				view.PointerMoved -= OnPointerMoved;
 				view.PointerReleased -= OnPointerReleased;
 				view.PointerCanceled -= OnPointerCancelled;
+				if (enableTouchEvents)
+				{
+					view.PointerEntered += OnPointerEntered;
+					view.PointerExited += OnPointerExited;
+					view.PointerPressed += OnPointerPressed;
+					view.PointerMoved += OnPointerMoved;
+					view.PointerReleased += OnPointerReleased;
+					view.PointerCanceled += OnPointerCancelled;
+				}
 			}
+		}
+
+		public void Detach(FrameworkElement view)
+		{
+			// clean the view
+			SetEnabled(view, false);
 
 			// remove references
 			onTouchAction = null;

source/SkiaSharp.Views.Forms/SkiaSharp.Views.Forms.iOS/SKCanvasViewRenderer.cs

@@ -9,6 +9,11 @@ namespace SkiaSharp.Views.Forms
 {
 	public class SKCanvasViewRenderer : SKCanvasViewRendererBase<SKFormsView, SKNativeView>
 	{
+		public SKCanvasViewRenderer()
+		{
+			SetDisablesUserInteraction(true);
+		}
+
 		protected override SKNativeView CreateNativeControl()
 		{
 			var view = base.CreateNativeControl();

source/SkiaSharp.Views.Forms/SkiaSharp.Views.Forms.iOS/SKGLViewRenderer.cs

@@ -13,6 +13,11 @@ namespace SkiaSharp.Views.Forms
 	{
 		private CADisplayLink displayLink;
 
+		public SKGLViewRenderer()
+		{
+			SetDisablesUserInteraction(true);
+		}
+
 		protected override SKNativeView CreateNativeControl()
 		{
 			var view = base.CreateNativeControl();

source/SkiaSharp.Views.Forms/SkiaSharp.Views.Forms.iOS/SKTouchHandler.cs

@@ -14,20 +14,35 @@ namespace SkiaSharp.Views.Forms
 		{
 			this.onTouchAction = onTouchAction;
 			this.scalePixels = scalePixels;
+
+			DisablesUserInteraction = false;
 		}
 
-		public void Attach(UIView view)
+		public bool DisablesUserInteraction { get; set; }
+
+		public void SetEnabled(UIView view, bool enableTouchEvents)
 		{
-			view.AddGestureRecognizer(this);
+			if (view != null)
+			{
+				if (!view.UserInteractionEnabled || DisablesUserInteraction)
+				{
+					view.UserInteractionEnabled = enableTouchEvents;
+				}
+				if (enableTouchEvents && view.GestureRecognizers?.Contains(this) != true)
+				{
+					view.AddGestureRecognizer(this);
+				}
+				else if (!enableTouchEvents && view.GestureRecognizers?.Contains(this) == true)
+				{
+					view.RemoveGestureRecognizer(this);
+				}
+			}
 		}
 
 		public void Detach(UIView view)
 		{
 			// clean the view
-			if (view != null)
-			{
-				view.RemoveGestureRecognizer(this);
-			}
+			SetEnabled(view, false);
 
 			// remove references
 			onTouchAction = null;